Page:Popular Science Monthly Volume 19.djvu/547

Rh My interpretation of the matter, to a certain extent, is this: That the visionary tendency is much more common among sane people than is generally suspected. In early life, it seems to be a hard lesson to an imaginative child to distinguish between the real and visionary world. If the fantasies are habitually laughed at, the power of distinguishing them becomes at length learned; any incongruity or nonconformity is noted, the vision is found out and discredited, and is no further attended to. In this way the tendency to see them is blunted by repression. Therefore, when popular opinion is of a matter-of-fact kind, the seers of visions keep quiet; they do not like to be thought fanciful or mad, and they hide their experiences, which only come to light through inquiries such as these that I have been making. But let the tide of opinion change and grow favorable to supernaturalism, then the seers of visions come to the front. It is not that a faculty previously non-existent has been suddenly evoked, but one that had been long smothered is suddenly allowed expression and to develop, without safeguards, under the free exercise of it.—Fortnightly Review.



ENTILATION is the supply of fresh air to an apartment, and the removal of impure or vitiated air therefrom. An adequate supply of free oxygen is absolutely necessary to animal life; and, the higher we ascend in the scale of that life, the greater the quantity of oxygen consumed, and the more urgent the necessity for its consumption. In the atmosphere this oxygen exists in a free state—in mechanical solution—and in the form and proportion in which it is most easily assimilable. From the atmosphere, the animal absorbs it by means of its breathing apparatus which provides for its absorption by the blood, and the blood carries it to the tissues. Pure air consists of a mechanical mixture of about four fifths nitrogen and one fifth oxygen, with traces of ammonia, and about one part in two thousand of carbonic-acid gas (CO2). These latter (ammonia and CO2), from their small amount, may be neglected.

Air becomes vitiated for breathing purposes by holding in solution other gases or substances whose presence interferes with the appropriation of oxygen by the animal, or, being themselves absorbed, exert a toxic influence upon the vital fluid and tissues of the body. Hence to secure an adequate supply of fresh air, and the removal of impurities that accumulate therein, are the objects of ventilation. In this paper school-room ventilation only will be considered.

A full-grown person breathes on an average about twenty times 